[jp1989]

Hi,
 New here and this is my first post. So I was wondering and my high school teacher wasn't able to explain it to me clearly...

What gives elements their properties? Why is it that oxygen is gaseous at room temperature or what makes gold a good conductor? Why is it that when a certain amount of atoms lump together they behave a certain way?

For example... I can crudely guess for instance that noble gases are gaseous because they don't share electrons, therefore they don't make bonds as easy as other elements but other properties are less clear...I'm guessing it has to do mostly with electrons because elements share characteristics periodically but I can't guess why some are metallic or shine different colors when excited.

Thanks a bunch. Xoxo from Mexico.

[mjc123]

Yup, it's electrons. Chemistry is all about electrons. Elements behave as they do because of the number and configuration of their electrons, and how they can (or can't) combine with those of other atoms. For instance, as you say, noble gases have stable configurations and are reluctant to form compounds; alkali metals have a single valence electron and readily form M⁺ cations etc. It's not always (or usually) as simple as that. We can have a good try at explaining the known chemical properties given the electron configuration, but it is much harder to work the other way around - to predict properties a priori from the electron configuration - to look at the periodic table and say e.g. "oh yes, element 79 will be a yellow metal and element 80 will be a liquid at room temperature".
Taking a step further back, it all comes down to mathematics - to the stable solutions of the Schrodinger equation for 1, 2, 3, 4... etc. electrons. It is one of the wonders of nature that simple mathematics produces such huge variety - take an element, add a proton and an electron (maybe a couple of neutrons) and you get an element with completely different properties.
To consider one of your questions, why is carbon a solid but N, O and F form diatomic gases? Well, carbon, having 4 valence electrons, can form 4 strong bonds to other carbon atoms and make structures like diamond and graphite, which are more stable than C₂ molecules. What kind of solid structures do you think N, O or F could form? How many bonds would they have, and how strong are these bonds compared to the X₂ molecules?

[jp1989]

Thanks for the clear and thought provoking response.
You made me realize now that although I may think elements have certain properties, such as number of valence electrons, it is actually the characteristics of their compounds that I had pondered about. It is not Oxygen that exist in our atmosphere, it is the oxygen molecule O₂ which is just as true and relevant as other oxygen containing compounds such as glucose or carbon dioxide.

Answering your question... Well the simplest approach was to combine N, F or O in diatomic molecules with heavier elements. This was really simple and kind of lame but I was to find they were crystalline
 Examples are Sodium Fluoride, Barite Oxide and Gallium Nitride.

I looked other possible compounds because diatoms were too simple and came across ammonia which is liquid and barium sulfate which is commonly used in the paints I use to make art.

Thanks again.

[mjc123]

Answering your question... Well the simplest approach was to combine N, F or O in diatomic molecules with heavier elements. This was really simple and kind of lame but I was to find they were crystalline. Examples are Sodium Fluoride, Barite Oxide and Gallium Nitride.

Actually I was thinking of the elements themselves, sorry if I wasn't clear. Basically it comes down to simple numbers. F, with 7 valence electrons, has a valency of 1, so can only form F₂ molecules, not extended structures. O, with a valency of 2, might conceivably form polymeric O-O-O-O- chains; but the O=O double bond is stronger than two O-O single bonds, which (together with the entropy of the gas) favours O₂ gas. Likewise N≡N is stronger than 3x N-N. But C₂ would have a double, not quadruple bond (you need MO theory to understand why), so forming 4 C-C bonds is favourable.